Electronic postage meters have been developed which include both a non-volatile memory which stores critical accounting information during non-use or power down conditions of the meter and a volatile random access memory. Meters of this type are described, for example, in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM and also in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS.
In meters of the above type, a firmware module, a read only memory, has a program which controls the operation of the postage meter. During operation of the meter, current operating information is written into a volatile random access memory. The information in the volatile random access memory is transferred to the non-volatile memory during a power down condition, as when the meter power switch is turned off and writes in the non-volatile memory with the updated data. When the meter is turned on again during a power up condition, the image of the data in the non-volatile memory is copied or written into the meter's volatile random access memory. As the meter is operated, the data in the volatile random access memory is modified in accordance with the usage. The critical accounting information stored in non-volatile memory may include, by way of example, the amount of postage remaining in the meter for subsequent printing (a descending register) and the total amount of postage printed by the meter (an ascending register). Other types of accounting or operating data may also be stored in the non-volatile memory. Examples of such other data may include a piece count register and a control sum register (the sum of the ascending and descending registers). The function served by the non-volatile memory circuits have replaced and enhanced the functions of the mechanical accounting registers or wheels utilized in previous mechanical meters.
In manufacturing meters of this type, the non-volatile memory which will contain the critical accounting information and operating data is secured in a tamper resistant housing. This housing includes various security measures, such as teltales and break-off screws, to insure that access to the non-volatile memory other and internal components cannot be achieved without leaving evidence of tampering. Accordingly, after the meter is assembled and when the meter is tested, if for any reason the register values are not proper or have values in them that are not desired, for example, due to testing, the only way that the non-volatile memory can be physically accessed is by taking apart the meter, which is a costly and time consuming process. Moreover, in certain countries outside the United States the problem is compounded since it is the practice to turn meters over to the postal authorities for testing with the meter's registers set to a non-initial number. The postal authorities test meters and run the registers from their non-initial number to a required (initial) reading before the meters are put in actual field service.